Circuit protection arrangement including coordinated operation of a circuit breaker and a current limiting fuse

ABSTRACT

A circuit protective arrangement which utilizes a circuit breaker and current limiting fuse to achieve reliable current interruption when connected to a source having an available current in excess of the rated current interruption rating of the circuit breaker. The source voltage is above the rated voltage of the circuit breaker device, as well as above the rated voltage of the fuse. A compact unitized structure for the circuit breaker and current limiting fuse is also shown for both single phase and multiphase installations.

C United States Patent [in 3,599,135

[72] Inventor gaaldE-(i y i w J 50 Field of Search. 337/6-8, a on egts. 3 [2 l] Appl. No. 1.958 [22] Filed Jan. 12. I970 [56] References Cited 1 1 Palenled s- 1971 UNITED STA rEs PATENTS ml Assign" E H5417? l l mu Stanback et al. 337/8 3.1 mm 1 was Schwab 337 7 M 3.070. 1 :8 1211962 Edmunds 337/6 647,999. June 22. 1967. now abandoned.

Prlnuln fixammer- Harold Broome Axmmnl brammer- Dewitt M. Morgan Arlarney-Ostrolenk. Faber, Gerb and Soffen ABSTRACT: A circuit protective arrangement which utilizes [54] OFA a circuit breaker and current limiting fuse to achieve reliable CIRCUIT BREAKER AND A CURRENT LIMITING current interruption when connected to a source having an FUSE available current in excess of the rated current interruption 9 Cl 6 D rating of the circuit breaker. The source voltage IS above the anus "wing rated voltage of the circuit breaker device, as well as above [52] [1.8. CI 337/6 the rated voltage of the fuse. A compact unitized structure for [5]] Int. 73/50, the circuit breaker and current limiting fuse is also shown for H0] h 85/54 both single phase and multiphase installations.

PATENTED AUG :0 l97| PATENTEDAUBIOIQT:

SHEET 2 BF 7 h mhml PATENTED AUG I 0 am SHEET 7 BF 7 wW H -WN I IHQNM CIRCUIT PROTECTION ARRANGEMENT INCLUDING COORDINATED OPERATION OF A CIRCUIT BREAKER AND A CURRENT LIMITING FUSE This application is a continuation of application Ser. No. 647,999, filed June 22, 1967 and now abandoned.

My invention relates to a circuit protection'arrangement which coordinates the interruption characteristics of a circuit breaker and current limiting fuse in a unique manner for increasing both the current and voltage values above the rated circuit breaker values.

It is known to series connect a circuit breaker and current limiting fuse device to increase the interruption capabilities of the series arrangement above that obtainable by the circuit breaker itself. As, for example, my copending Pat. application Ser. No. 549,207, filed May 11, 1966, entitled Circuit Breaker Trip Unit Assembly with Improved Thermal Characteristics," new issued as U.S. Pat. No. 3,356,805 dated Dec. 5, i967; and U.S. Pat. No. 2,843,702, issued July 15, 1958, in the name of William Harold Edmunds, entitled Protective Device with Current Limiting Means," both assigned to the assignee of the instant invention, disclose such previous circuit protective arrangements. ln such prior arrangements, the coordination between the interruption characteristics of the circuit breaker and current limiting fuse had been selected to increase the fault current capabilities above the circuit breaker current rating, with the voltage of the source being no greater than the voltage of the circuit breaker. That is, the circuit breaker is intended to interrupt all magnitude of overcurrent and fault currents up to its maximum permissible rated interruption current value. Should a severe short circuit occur, the magnitude of which exceeds the interruption current rating of the circuit breaker, the current limiting fuse will be rapidly actuated, thereby serving to interrupt the fault current associated with the phase in which it occurs. Such actuation of the current limiting fuse reduces the current flow to a lesser magnitude of let-through current to a value which may be safely handled by the circuit breaker unit and serves to provide rapid followup actuation of the circuit breaker.

In such prior art coordinated operation of the circuit breaker and current limiting fuse device, it has been necessary to include a circuit breaker having a voltage rating at least equaling the voltage rating of the source. While this may have proved practical for large installations having substantial panelboard space available, the bulkiness of a, higher voltage rated circuit breaker has necessitated excessive space requirements in many applications. More specifically, in many present day I lighting or moderate capacity distribution systems, the available energy has increased to a magnitude that has required large circuit breakers and cumbersome panel installations to provide proper protection. My-invention aptly solves this requirement by the unique coordination of the circuit breaker device and current limiting fuse to provide an assembly that has both a higher current and voltage interrupting capabilities than the circuit breaker or fuse by itself, and thereby permits the utilization of a smaller frame size circuit breaker.

More specifically, the interruption characteristics of the circuit breaker and current limiting fuse are predeterminately coordinated such that their crossover point is significantly below the maximum permissible rated interrupting current of the circuit breaker. The crossover interrupting current value is selected upon an energy consideration, such that the circuit breaker will never be subjected a kva. magnitude beyond its rated kva. capacity. Hence, when this series combination is now subjected to a severe fault current at the source voltage (which will be above the rated circuit breaker voltage), the fuse operates at this crossover interruption current (which is below the circuit breaker rated interruption current). The operation of the fuse is associated with an appreciable counter emf across the fuse and a limiting of the circuit current to a let-through value. Thus, the breaker is prevented from receiving its maximum rated current at the higher source voltage.

The let-through current can be safely handled by the circuit breaker, and is of a magnitude to insure rapid followup actuation of the circuit breaker operating means. This is of particular importance in multiphase installations wherein the circuit breaker operating means of the individual phase units are appropriately interconnected to avoid single phasing.

In accordance with another aspect of my-invention, a compact unitized assembly is disclosed, which contains both the circuit breaker operating components and the current limiting fuse. The circuit breaker is illustratively shown as being of the same general type disclosed in U.S. Pat. No. 2,996,589, issued Aug. 15, 1961, in the name of F. E. Myers, entitled "Pivotal Bimetal, and assigned to the assignee of the instant invention.

My novel unitized structure provides an extremely simple arrangement for the insertion or removal of the current limiting fuse. Appropriate coordination is provided between the fuse holder and the circuit breaker device, as is the subject of U.S. Pat. Application Ser. No. 648,062 filed on even date herewith, in the name of F. E. Myers, and entitled Fuse Holder lncluding Coordinated Operating Means Between Fuse Insertion and an Associated Circuit Breaker Device," issued Oct. 2l, i969 as U.S. Pat. No. 3,474,373 This fuse holder includes means for automatic actuation of the circuit breaker to the contact disengaged condition upon the removing of the current limiting fuse. Further, the current limiting fuse may only be inserted in the unitized structure, while the circuit breaker device is in the contact disengaged condition.

The fuse receiving compartment of the novel unitized structure also preferably includes means for insuring that the proper size fuse is being inserted. This aspect of the structure is the subject of U.S. Pat. Application Ser. No. 648,049 filed on even date herewith, and entitled Noninterchangeable Means for Circuit Breaker Fuse Connections, issued Oct. 6, 1970 as U.S. Pat. No. 3,533,038.

It is therefore seen that the basic concept of the instant invention resides in the unique coordination of a current breaker device and current limiting fuse to provide circuit protection of both a higher current and voltage interruption capacity than the circuit breaker or fuse by itself. An interrelated concept of the invention is to provide ;an extremely practical and compact unitized assembly, incorporating the circuit breaker device and current limiting fuse.

It is therefore a primary object of may invention to provide a circuit protective arrangement for increasing the voltage interruption capabilities of a circuit breaker device.

A further object of my invention is to provide a circuit protective arrangement including a series connected circuit breaker device and current limiting fuse device, in which the interruption characteristics of said devices are predeterminately coordinated to raise both the current and voltage interruption capabilities of the combination, over that achievable by either unit alone.

A more specific object of my-invention is to provide such a circuit protective arrangement, in which the interruption characteristics of the circuit breaker device and current limiting fuse device crossover at a predetermined fuse interrupting current value which is significantly less than the circuit breaker rated interruption current.

Another object of my invention is to provide a circuit protective arrangement, including the coordinated operation of a circuit breaker device and current limiting fuse device, which is intended for operation in conjunction with a source having an available voltage and fault current in excess of the circuit breaker ratings, and the current limiting fuse serves to lower the maximum interruption current of the circuit breaker to a value below the rated circuit breaker interruption current value.

An additional object of my invention is to provide such coordinated operation of a current limiting fuse device and circuit breaker device, in conjunction with a source voltage above the rated circuit breaker voltage, in which the current limiting fuse device prevents the maximum'interruption enerbreaker kva. capacity.

Still a further object of my invention is to provide a compact unitized device, in accordance with the above-mentioned operating objectives, in which the circuit breaker mechanism and current limiting fuse are structurally and operatively interrelated.

Still another object of my invention is to provide such a coordinated device, in which the current limiting fuse is readily accessible and may be rapidly removed and replaced.

These as well as other objects of my invention will become readily apparent upon a consideration of the following description and drawings, in which:

FIG. 1 isa simplified perspective view, showing the unitized device constructed in accordance with the objectives of the instant invention, and showing the manner in which the fuse may be readily inserted within its compartment.

FIG. 1A is a schematic showing the unitized device of FIG. 1 connected in circuit with a source of electrical energy.

FIG. 2 is a front view, with the cover removed and the fuse inserted, showing the coordinating circuit breaker device and current limiting fuse, in the contact engaged condition.

FIG. 3 shows a subassembled portion of the unitized device, including the movable contact arm, thermal and .magnetic sensing means, and one of the fuse terminals.

FIG. 4 is a top view, taken along the line 4-4 of FIG. 2, with the cover replaced.

FIG. 5 is a side view taken in the direction of line 5-5 of FIG. 2.

FIG. 6 is a detailed view, showing the manner in which the current limiting fuse in its fuse-holder may be readily inserted into its respective compartment.

FIG. 7 is a simplified representation of FIG. 2, and showing the manner in which the removal of the fuse starts to bring the circuit breaker device towards its tripping condition.

FIGS. 8 and 9 sequentially follow FIG. 7 and show the manner in which actual tripping of the circuit breaker is effected during the removal operation of the current limiting fuse.

FIGS. 10 and 11 are front and top views, respectively, of the fuse holder.

FIG. 12 shows the condition wherein the overload tripping mechanism of the circuit breaker has operated to move the contacts to their disengaged condition. This condition may correspond to the presence of a moderate overload or fault condition, intended to be operated by the circuit breaker thermal or magnetic trip; or the followup actuation of the circuit breaker by the let-through current after the operation of the current limiting fuse. The interpole mechanism for multiphase operation is also shown. 7

FIG. 13 is a top view showing a three-pole assembly of unitized devices, constructed in accordance with my invention.

FIG. 14 is an end view, similar to FIG. 5, of such a threepole assembly.

FIG. 15 graphically shows the manner in which the operating characteristics of the current limiting fuse and circuit breaker device are predeterminately coordinated in accordance with the objectives of my invention.

Referring initially to FIGS. 1-5, the single phase embodiment of a unitized circuit protective device is shown. The device includes a molded housing, including a base section 22, and a complementary cover 24. The housing sections are held together by rivets 26.

The molded housing thus includes a pair of opposed top and bottom walls 30, 32 respectively; a pair of opposed first and second sidewalls 34, 36, respectively; and a pair of opposed front and rear walls 38, 40, respectively. The internal volume bounded by the above'noted walls 30, 32, 34, 36, 38 and 40 is separated into two compartments by a dividing region, generally shown by the dotted line 42. The first compartment 44 includes a circuit breaker device, generally constructed in accordance with the generalteachings of aforementioned U.S. Pat. No. 2,996,589. The longitudinally adjacent second compartment 46 contains the current limiting fuse 50, which is appropriately circuit connected to the circuit breaker device, in a manner which will henceforth be described, so as to provide a series circuit connection therebetween.

Unitized device 20 includes an external line terminal 100, which is connected to an external source of electrical energy 530 (FIG. 1A) in the conventional manner. This terminal is shown as a bolt-type terminal; however, it should be understood that a plug-in-type terminal, as shown in aforementioned U.S. Pat. No. 2,996,589, may alternatively be employed. Load terminal is provided at the opposite side of the circuit breaker device 20 for connection to an external load (not shown). The circuit breaker device within compartment 44 is advantageously of a type which has achieved widescale utilization for home and light industrial use, and has advanced to the point where it is extremely reliable and efficient in operation, and may be rapidly and economically manufactured. It is, however, to be understood that my invention is not limited to the utilization of such a circuit breaker, and the unique manner in which I coordinate the interruption characteristics of the circuit breaker and current limiting fuse may be achieved in conjunction with other circuit breaker structures.

Compartment 44 includes a plurality of recesses for receiving and locating the various operating components of the circuit breaker. Located within these recesses is a stationary contact 102, which is connected to line terminal 100, via conductive member 101. Cooperating with stationary contact 102, is a movable contact 104, mounted to the lower end of a bifurcated contact arm 106. Parallel plate arc extinguishing means 108 is provided within recesses 109. The upper bifurcated end of contact arm 106 abuts a suitable pivot formation of internally extending portion 112 of manual operating member 114. Manual operating member 114 is pivoted about a housing protrusion 113, which is entered into suitable aligned recesses of the molded base 22 and cover 24. The manual operating member includes an outwardly extending portion 116 for manually moving the circuit breaker between its manual OFF and manual ON positions in the manner fully set forth in aforementioned U.S. Pat. No. 2,996,589.

Contact carrying arm 106 has a braid member 120, secured thereto, with the opposite end of the braid member being connected to braid lug 122. The electrical path then continues through bimetal 124, braid 126, conductor 128, to the electromagnetic coil 130. Electromagnetic coil is, in turn, electrically connected via conductor 131 to fuse receiving terminal clip 132. The circuit then continues through current limiting fuse device 50, to the opposite fuse terminal clip 134, which is connected to externally accessible load terminal 110.

Thus, it should be recognized that device 20 includes a series circuit path from line terminal 100, via stationary and movable contacts 102, 104, bimetal 124, electromagnetic trip coil 130 and fuse 50, terminating at the load terminal 110.

FIG. 3 represents a subassembled portion of the unitized device 20, which includes the movable contact arm (106), the thermal (124) and magnetic (130) trip member of the circuit breaker portion; and fuse clip terminal 132 of the current limiting fuse portion. The series connection between the circuit breaker and fuse is provided by conductor member 131. It should be understood that the use of such a subassembly permits considerable manufacturing efficiencies in the assembly of the coordinated circuit breaker and current limiting fuse device 20, as well as permitting an extremely compact unit.

The operating mechanism for bringing about the engagement and disengagement of cooperating contacts 102, 104 comprises a latchable cradle member 140, which is pivotally mounted at one end thereof, to base protrusion 142. Cradle also carries a kicker 145, which gives contact arm 106 a hammerlike blow during the tripping operation to insure separation of the circuit breaker contacts.

One end of an operating spring 148 is connected to cradle 140 at aperture 150, while the other end of operating spring 148 is connected to contact arm 106 at aperture 152. Operating spring 148 is always in tension, thereby urging contact arm end 115 upwardly into engagement with its pivotal mounting to manual operating member 114, and latchable cradle member 140 clockwise about its pivotal mounting 142; The force of operating spring 148 relative to the pivotal mounting of contact arm 106 also serves to urge the movable contact 104 into firm engagement with its cooperating stationary contact 102, as shown in FIG. 2.

Latchable'cradle member 140 includes a latchable tip 144, which seats upon latch portion 154, carried by the lower end of the elongated bimetallic member 124. A bearing pin 156 is suitably secured to an intermediate region of elongated bimetallic member 124, as by welding, and enters suitable circular recesses of the circuit breaker base 22, and cover 24, for pivotally mounting the bimetallic element. The bimetallic element 124 is biased in a clockwise direction about its pivot 156 by spring 158. Calibrated adjustment of the trip unit is obtained by calibrating screw 160, which bears against intermediate connecting member 162.

The electromagnetic actuation of the circuit breaker device is provided by coil 130, in conjunction with pole pieces 164, which upon actuation draws the armature member 166 towards the pole pieces. As the armature .member 166 is drawn towards the pole pieces, its upper end 168 will strike the lower end of bimetallic member 124, thereby moving it in the direction shown by arrow 170. Further, the sustaining of a moderate overload condition similarly deflects the elongated bimetallic element in the same direction of arrow 170. Such movement of the lower end of the bimetallic element 124 serves to effect releasing of the latched engagement between cradle tip 144 and latch member 154, so as to bring the circuit breaker mechanism to the overload tripped condition, as shown in FIG. 12..

An aperture 172 is provided for interpole tripping ofa multiphase assembly. FIG. 12 shows the addition of such an interpole trip means, which includes an individual pole tripping member 174, pivotally mounted to bearing pin 156. Tripping member 174 includes a rectangular aperture 176, which receives an interpole trip bar 178, for coordinating the operation of the individual phase circuit breaker mechanisms. That is, the tripping of one of the phases will cause member 180 mounted to the cradle of that phase to engage its tripping member 174, and rotate it counterclockwise about pivot member 156. This movement of the tripping member will, in turn, be transmitted to the other phases, via trip bar 178, thereby similarly rotating the tripping members 174 of the other phases counterclockwise against their elongated bimetallic elements 124, which serves to effect tripping operation of the other phases.

Fuse 50 is inserted within an externally accessible opening 182 along the top wall 30 of compartment 46. This manner of inserting or removing the fuse 50 is extremely convenient, since the top surface 30 (including the outwardly extending manual operator 116) is normally accessible when the device is mounted within its panelboard location.

Fuse 50 includes opposed end ferrule terminals 184, 186, which when inserted in compartment 182 are electrically connected to fuse clip terminals 132, 134, respectively. A noninterchangeability means, in the form of an insulative tube 187, is provided to prevent contact being made by a current limiting fuse ofimproper rating. For a further description of noninterchangeability means 187 and its mode of operation, reference is made to aforementioned 115. Pat. No. 3,533,038. Fuse 50 is retained within a rotatable fuse holder 190, which includes a star-type resilient washer 192, for frictionally engaging the ferrule end terminal 184 of the fuse.

An interlock trip lever 194 pivotally mounted at 196 cooperates with the cam surface 200 of the fuse holder, in the manner which is the subject of above-mentioned US. Pat. No. 3,474,373 to coordinate the tripping of the circuit breaker to the insertion and removal of the fuse 50. It is sufficient to recognize for the purposes of the instant application that interlock lever 194 is biased counterclockwise about its pivot 196, by spring member 198, such that the end 201 thereof is urged into engagement with the lower end of the bimetallic element 124. This counterclockwise movement of interlock lever 194 is restrained by the abutting engagement of cam follower protrusion 202 at the opposite end of interlock lever, with the annular cam surface 200 provided along the bottom of rotatable fuse holder 190. With the fuse fully inserted as shown in FIG. 2, the interlock lever 194 is moved clockwise against the biasing action of spring 198 to its clockwise extreme, so as to prevent the engagement of end 201 with the elongated bimetal. Rotation. of the fuse holder in the direction for removal of the fuse permits counterclockwise movement of the interlock lever 194 about pivot 196, in the manner sequentially shown in FIGS. 7, 8 and 9. That is, as the cam follower 202 moves from the cam surface position 200-1 of FIG. 2, to the position 200-2 of FIG. 7, end 201 comes into engagement with the lower end of the bimetallic element 124. Further movement thereof to cam surface 200-3 (FIG. 8) causes sufficient counterclockwise movement of interlock lever 194 and end 201 against the bimetal to defeat the latched engagement of cradle tip 144 with latch member 154. The circuit breaker mechanism will thus be in TRIP condition when the fuse holder is in a position to permit fuse removal, as shown in FIG. 9.

In order to provide proper safety, the cam surface 200 is interrelated in conjunction with the movement of interlock lever 194, such that tripping of the circuit breaker mechanism will occur upon the first forty-five degrees of counterclockwise rotation of fuse holder 190 (FIG. 8), wherein 90 of rotation is required to remove the fuse holder (FIG. 9). Thus, removal of the fuse will always be accompanied by tripping of the circuit breaker, and in multiphase assemblies with the tripping of the associated phases. Conversely, the fuse 50 may only be inserted in device 20, when the circuit breaker portion thereof is in the contact disengaged condition.

The illustrated fuse holder, which is more fully discussed in aforementioned U.S. Pat. No. 3,474,373 includes appropriate registry means to guide the insertion of the fuse. This is achieved by fuse holder protrusions 210 and 211, which must be aligned with housing slots 212 and 213. The fuse assembly may then be pushed down, to the point where the protrusions 210 and 211 meet annular guide slides within the fuse compartment 46, to assist the rotation of the fuse holder 190 to the fully inserted condition, wherein cam follower 202 abuts fuse holder cam surface 200-1.

Reference is now directed to FIGS. 13 and 14, which show a three-phase assembly, in which each of the phases is constructed in accordance with the instant invention. The individual phase unitized devices are indicated by the numbers 20-1, 20-2, and 20-3, each of which generally correspond to the structure discussed in conjunction with FIGS. 112 above, with the suffix notations-l4 1, -2, and -3 for the line and load terminal indicating reference numerals being used to indicate the particular phase involved. The individual fuses are inserted by virtue of fuse holders -1, 190-2, and 190-3. Coordinated operation between the phases is obtained by virtue of the interpole tripping arrangement (shown in FIG. 12).including elements 174, 178 and 180. The manual operating handles of the circuit breaker mechanisms are appropriately tied together by virtue of interconnecting member 225.

A commercial three-pole unit, in accordance with FIGS. 13 and 14, may be 3 inches wide, 3% inches high, and 2% inches deep. Such a three-pole unit can safely interrupt up to 100,000 amperes 277/480 Volts. Thus, it should be readily appreciated that a compact size circuit protection arrangement is provided which is capable of reliable protection in modern lighting and moderate distribution systems, which have experienced substantially increased available source energies.

Reference is now made to FIG. 15, which graphically illustrates the interruption characteristics of the circuit breaker and current limiting fuse, and the manner in which they are predeterminately coordinated to achieve the instant objectives. Current magnitude is indicated by the abscissa 300 and the tripping time by the ordinate 310. The 100 percent load current is shown by line 320'At all values of load current up to the magnitude indicated by the line 320, there should not be any interruption..As the current exceeds the 100 percent load value, the circuit breaker device indicated by curve .325 begins to operate. Between. the region generally bounded by 527 and 329, the thermal trip of the breaker is operative, in accordance with its well-known inverse time characteristic to trip the breaker. That is, under a moderate overloadcondition, the deflective movement of the elongated bimetallic element 124 serves to effect tripping of the circuit breaker device. A,s the fault current increases beyond the magnitude indicated by point 329, the actuation'of the circuit breaker magnetic trip assembly is more rapid than the thermal trip, and hence interruption of the load current is controlled by the magnetic trip. in the absence of the current limiting fuse, the breaker is designed to safely interrupt a maximum permissible interruption current indicated at 340 at a specific rated voltage. In accordance with previous coordinated operation of a circuit breaker device and current limiting fuse, the crossover point of the fuse characteristic and the circuit breaker was selected to occur at point 340. That is, the breaker had been previously utilized to interrupt currents up to its maximum interruption current value, with the currentlimiting fuse operable upon the occurrence of greater currents. However,.this previous arrangement required that the circuit breaker could not be used to interrupt such rated interruption currents at any voltage in excess of the voltage rating of the breaker, or else its kva. rating would be exceeded and the breaker would be required to interrupt a greater available energy than it was designed for. Thus, the breaker voltage rating had to at least equal the source voltage.

ln contradistinction to the previous arrangements, the current limiting fuse interruption characteristic, 350, of my invention is predeterminately selected to intersect the circuit breaker interruptioncharacteristic at a point 331, which is intentionallyselected to be significantly less than the circuit breaker rated interruption current (340). Thus, the breaker may now be used in conjunction with the current limiting fuse, for the protection ofa circuit having a source voltage in excess of the circuit breaker rated voltage.

Considering now the operation of my circuit protective arrangement, when the current magnitude reaches the value indicated by point 331, the current limiting fuse operates, drawing an arc and adding resistance to the circuit. The current limiting fuse now acts as a counter EMF opposing the source voltage, and decreasing the voltage drop across the series connected circuit breaker. In this manner, the current magnitude through the breaker is reduced to a lower let-through value, which maybe safely interrupted'by the breaker at the reduced voltage drop across the breaker. The manner in which the current limiting fuses 50 acts as such a counter EMF is determined by the proper selection of its link dimensions, filler material and spacing, as well as the distance between the end terminals 184, 180 to obtain the required melting time.

A typical arrangement device in accordance with my improved circuit protection technique utilizes a 300-vo1t current limiting fuse in conjunction with a 240-volt circuit breaker. The fuse may be the type G60 time delay fuse manufactured by the Chase Shawmut Company of Newburyport, Mass. The IMO-volt rating of the circuit breaker is determined by such structural features thereof as contact separation, contact materials, bimetal materials, are chute structure and magnet structure. increasing the voltage rating of the circuit breaker would require the modification of the structural aspects thereof, and in particular increasing the contact separation. Where the rated interruption current of the breaker at 240 volts may typically be 100,000 amperes, crossover point 331 may be in the order of 1500 amperes lt is to be understood that these typical parameters are only illustrative, and are no means intended as being a limited application of the herein claimed inventive concept.

it is therefore, seen that my invention provides an improved circuit protection arrangement, which coordinates the interruption characteristics of a circuit breaker device and current limiting fuse, in a unique manner, to provide higher current and voltage interruption capabilities. Although I have herein described a preferred embodiment of my novel invention both as a single phase and multiphase device, many variations and modifications will now be apparent to those skilled in the art, and I- therefore prefer to be limited not by the specific disclo' sure herein but only by the appending claims.

The embodiments of the invention in which an exclusive privilege property is claimed are defined as follows:

1. A combination comprising:

a source of electrical energy and a protective arrangement connected in circuit with said source for automatically interrupting flow of current from said source to an external load upon the occurrence of predetermined fault conditions;

said protective arrangement including the series combination of a circuit breaker and current limiting fuse;

said circuit breaker including a pair of cooperating contacts, and an operating means for moving said contacts between their engaged and disengaged conditions, responsive to predetermined fault conditions; 7

said circuit breaker having a predetermined interruption characteristic, and a maximum permissible rated interruption current value at a rated voltage value to define its maximum kva. capacity;

said rated interruption current value being less than the maximum current available from said source;

said current limiting fuse having a rated voltage value and a predetermined interruption characteristic;

the improvement comprising predeterminately coordinating the interruption characteristics of said circuit breaker and current limiting fuse such that said rated voltage values of said fuse and said circuit breaker are each significantly less than the voltage of said source, and in said series combination, said current limiting fuse interrupts at a predetermined fuse interrupting current value;

said predetermined fuse interrupting current value being significantly less than said circuit breaker rated interruption current, thereby preventing the subjection of said circuit breaker to an interruption current in excess of said predetermined fuse interrupting value, at said voltage of said source.

2. A combination as set forth in claim 1, in which:

the kva. value of said predetermined fuse interrupting current value at said voltage of said source is no greater than the breaker kva. capacity.

3. A combination as set forth in claim 1, in which:

said current limiting fuse, upon interruption, having an appreciable voltage drop in opposition to the voltage of said source;

said appreciable voltage drop serving to reduce the voltage drop across said circuit breaker with the let-through current of said interrupted fuse being sufficient to provide rapid followup operation of said circuit breaker operating mean to the contact disengaged condition;

said followup operation of said circuit breaker contacts being at a circuit breaker voltage appreciably less than the voltage of said source.

4. A combination as set forth in claim 1, also comprising:

a unitary housing including having a dividing region defining the boundary between adjacent first and second compartments;

said unitary housing including a pair of opposed top and bottom walls, a pair ofopposed first and second sidewalls, and a pair of opposed front and rear walls;

the distance between said opposed pair of front and rear walls being substantially less than the distance between any of the other pairs of opposed walls;

said dividing region extending parallel to said sidewalls and being substantially closer to said second sidewall than said first sidewall;

said first compartment bounded by said first sidewall, said dividing region, said top wall, bottom wall, front wall and rear wall;

said adjacent second compartment bounded by said dividing region, second sidewall, said-top wall, bottom wall, front wall and rear wall;

said first compartment containing said circuit breaker including said pair of cooperating contacts and said operating means for moving said contacts between their engaged and disengaged conditions;

said second compartment including means removably receiving said current limiting fuse and mounting same substantially parallel to said sidewalls; and

circuit means extending between said compartments for electrically connecting said circuit breaker to said current limiting fuse.

5. A combination as set forth in claim 4, in which:

a line terminal connecting means at said first sidewall connects said circuit breaker to said source; I

a load terminal connecting means at said second sidewall for connecting said current limiting fuse to an external load;

said circuit means series circuit connecting said circuit breaker and current limiting fuse, such that said circuit breaker and current limiting fuse are series circuit connected between the line and load terminals.

6. A combination as set forth in claim 4, in which:

said circuit breaker includes a manually operable handle extending out of said top wall;

said second compartment including an access opening at said top wall;

a fuse holder for said current limiting fuse, insertable into said second compartment through said access opening.

7. A combination as set forth in claim 1, in which:

said circuit breaker and said current limiting fuse in combination constitute a first circuit protective device;

at least one other circuit protective device, of substantially identical construction to said first circuit protective device, connected in circuit with said source for automatically the flow of current from said source to an external load upon the occurrence of predetermined fault conditions;

said circuit protective devices being stacked side by side;

a common element extending between said protective .devices and operatively interconnecting same whereby the actuation of one of said protective devices is operatively transmitted to the remaining devices for coordinated actuation thereof;

said current limiting fuse, upon interruption, having an appreciable voltage drop in opposition'to the voltage of said source with said appreciable voltage drop serving to reduce the voltage drop across said circuit breaker, and the let-through current of said interrupted fuse being sufficient to provide rapid followup operation of said circuit breaker operating means to the contact disengaged condition;

said followup operation of said circuit breaker contacts being at a circuit breaker voltage appreciably less than said voltage of said source;

said common element responsive to the followup operation of the actuated phase and transmitting an interpole tripping signal to the remainingcircuit breakers for coordinated movement to their contact disengaged condition.

8. A combination as set forth in claim 7, in which:

each of said protective devices is a self-supporting assembly contained within a unitary housing, and forming a unitized assembly of a single pole circuit breaker and current limiting fuse;

I interpole connectingmeans for maintaining the desired 9. A combination as set forth in claim 8, in which: said unitary housing including a pair of opposed top and bottom walls, a pair of opposed first and second sidewalls, and a pair of opposed front and rear walls;

said individual protective devices being stacked parallel to said front and rear walls;

the distance between said opposed pair of front and rear walls substantially less than the distance between any of the other pairs of opposed walls;

a dividing region, extending parallel to said sidewalls and defining the boundary between said first and second compartments;

said dividing region being substantially closer to said second sidewall than said first sidewall;

said first compartment bounded by said first sidewall, said dividing region, said top wall, bottom wall, front wall and rear wall;

said adjacent second compartment bounded by said dividing region, second sidewall, said top wall, bottom wall, front wall and rear wall;

said first compartment containing said circuit breaker;

said second compartment adapted to removably receive said current limiting fuse and mounting same substantially parallel to said sidewalls;

.circuit means extending between said compartments for electrically connecting said circuit breaker to said current limiting fuse. 

1. A combination comprising: a source of electrical energy and a protective arrangement connected in circuit with said source for automatically interrupting flow of current from said source to an external load upon The occurrence of predetermined fault conditions; said protective arrangement including the series combination of a circuit breaker and current limiting fuse; said circuit breaker including a pair of cooperating contacts, and an operating means for moving said contacts between their engaged and disengaged conditions, responsive to predetermined fault conditions; said circuit breaker having a predetermined interruption characteristic, and a maximum permissible rated interruption current value at a rated voltage value to define its maximum kva. capacity; said rated interruption current value being less than the maximum current available from said source; said current limiting fuse having a rated voltage value and a predetermined interruption characteristic; the improvement comprising predeterminedly coordinating the interruption characteristics of said circuit breaker and current limiting fuse such that said rated voltage values of said fuse and said circuit breaker are each significantly less than the voltage of said source, and in said series combination, said current limiting fuse interrupts at a predetermined fuse interrupting current value; said predetermined fuse interrupting current value being significantly less than said circuit breaker rated interruption current, thereby preventing the subjection of said circuit breaker to an interruption current in excess of said predetermined fuse interrupting value, at said voltage of said source.
 2. A combination as set forth in claim 1, in which: the kva. value of said predetermined fuse interrupting current value at said voltage of said source is no greater than the breaker kva. capacity.
 3. A combination as set forth in claim 1, in which: said current limiting fuse, upon interruption, having an appreciable voltage drop in opposition to the voltage of said source; said appreciable voltage drop serving to reduce the voltage drop across said circuit breaker with the let-through current of said interrupted fuse being sufficient to provide rapid followup operation of said circuit breaker operating means to the contact disengaged condition; said followup operation of said circuit breaker contacts being at a circuit breaker voltage appreciably less than the voltage of said source.
 4. A combination as set forth in claim 1, also comprising: a unitary housing including having a dividing region defining the boundary between adjacent first and second compartments; said unitary housing including a pair of opposed top and bottom walls, a pair of opposed first and second sidewalls, and a pair of opposed front and rear walls; the distance between said opposed pair of front and rear walls being substantially less than the distance between any of the other pairs of opposed walls; said dividing region extending parallel to said sidewalls and being substantially closer to said second sidewall than said first sidewall; said first compartment bounded by said first sidewall, said dividing region, said top wall, bottom wall, front wall and rear wall; said adjacent second compartment bounded by said dividing region, second sidewall, said top wall, bottom wall, front wall and rear wall; said first compartment containing said circuit breaker including said pair of cooperating contacts and said operating means for moving said contacts between their engaged and disengaged conditions; said second compartment including means removably receiving said current limiting fuse and mounting same substantially parallel to said sidewalls; and circuit means extending between said compartments for electrically connecting said circuit breaker to said current limiting fuse.
 5. A combination as set forth in claim 4, in which: a line terminal connecting means at said first sidewall connects said circuit breaker to said source; a load terminal connecting means at said second sidewall for connecting said current limiting fuse to an external load; said circUit means series circuit connecting said circuit breaker and current limiting fuse, such that said circuit breaker and current limiting fuse are series circuit connected between the line and load terminals.
 6. A combination as set forth in claim 4, in which: said circuit breaker includes a manually operable handle extending out of said top wall; said second compartment including an access opening at said top wall; a fuse holder for said current limiting fuse, insertable into said second compartment through said access opening.
 7. A combination as set forth in claim 1, in which: said circuit breaker and said current limiting fuse in combination constitute a first circuit protective device; at least one other circuit protective device, of substantially identical construction to said first circuit protective device, connected in circuit with said source for automatically interrupting the flow of current from said source to an external load upon the occurrence of predetermined fault conditions; said circuit protective devices being stacked side by side; a common element extending between said protective devices and operatively interconnecting same whereby the actuation of one of said protective devices is operatively transmitted to the remaining devices for coordinated actuation thereof; said current limiting fuse, upon interruption, having an appreciable voltage drop in opposition to the voltage of said source with said appreciable voltage drop serving to reduce the voltage drop across said circuit breaker, and the let-through current of said interrupted fuse being sufficient to provide rapid followup operation of said circuit breaker operating means to the contact disengaged condition; said followup operation of said circuit breaker contacts being at a circuit breaker voltage appreciably less than said voltage of said source; said common element responsive to the followup operation of the actuated phase and transmitting an interpole tripping signal to the remaining circuit breakers for coordinated movement to their contact disengaged condition.
 8. A combination as set forth in claim 7, in which: each of said protective devices is a self-supporting assembly contained within a unitary housing, and forming a unitized assembly of a single pole circuit breaker and current limiting fuse; interpole connecting means for maintaining the desired number of said unitized assemblies in stacked, side-by-side arrangement for coordinated multipole operation.
 9. A combination as set forth in claim 8, in which: said unitary housing including a pair of opposed top and bottom walls, a pair of opposed first and second sidewalls, and a pair of opposed front and rear walls; said individual protective devices being stacked parallel to said front and rear walls; the distance between said opposed pair of front and rear walls substantially less than the distance between any of the other pairs of opposed walls; a dividing region, extending parallel to said sidewalls and defining the boundary between said first and second compartments; said dividing region being substantially closer to said second sidewall than said first sidewall; said first compartment bounded by said first sidewall, said dividing region, said top wall, bottom wall, front wall and rear wall; said adjacent second compartment bounded by said dividing region, second sidewall, said top wall, bottom wall, front wall and rear wall; said first compartment containing said circuit breaker; said second compartment adapted to removably receive said current limiting fuse and mounting same substantially parallel to said sidewalls; circuit means extending between said compartments for electrically connecting said circuit breaker to said current limiting fuse. 